Changes in Ownership Interests (Detail)	9 Months Ended			9 Months Ended
	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Lazard Ltd [Member]	Sep. 30, 2011 Lazard Ltd [Member]	Sep. 30, 2012 LAZ-MD Holdings [Member]	Sep. 30, 2011 LAZ-MD Holdings [Member]
Change In Ownership Interest [Line Items]
Beginning balance (in shares)	127,350,561	129,766,090	129,766,090	123,009,311	119,697,936	6,756,779	7,652,625
Common membership interest activity in connection with: Exchanges for Class A common stock				191,701	738,655	(191,701)	(738,655)
Business acquisitions	2,434,561				2,434,561
Repurchase of common membership interests from LAZ-MD Holdings	(19,032)						(19,032)
Ending balance (in shares)	129,766,090	129,766,090	129,766,090	123,201,012	122,871,152	6,565,078	6,894,938
Percentage of Ownership Beginning Balance				94.80%	94.00%	5.20%	6.00%
Percentage of Ownership Ending Balance				94.90%	94.70%	5.10%	5.30%